To determine whether tachyphylaxis contributes to the failure of NIDDM patients glycemic control is poor despite maximal therapeutic doses of "second generation" sulfonylureas. To assess the effect of dose frequency each patient will be followed for 9 months, 3 months each on 10 mg BID, 10 mg PD, and 10 mg QOD of PO glyburide with mixed meal challenge tests at the end of each 3 month phase.